Manufacture of phenols or salts thereof



Patented Oct. 26, 1948 PHENOLS OR SALTS REOF MANUFACTURE OF THE Daniel Tyrer, Stoekton-on-Tees, England No Drawing.

This invention relates to the manufacture of phenols or salts thereof from salts of the corresponding sulphonic acids.

This application is a continuation-in-part of my copending application Serial No. 493,924, filed July 8, 1943, now U. S. Patent 2,407,045, issued September 3, 1946.

The customary fusion process for the manufacture of phenols from the corresponding sulphonic acids involves fusing the sulphonic acid salt with caustic alkali, and the reaction in the case of sodium benzene sulphonate, which may be taken as typical, is as follows:

Thus, 2 molecular proportions of caustic soda are theoretically required for 1 molecular proportion of sulphonate, but in practice it is customary to use 2 /2 molecular proportions or more. In the manufacture of resorcinol from sodium benzene- 1:3disulphonate 4 molecular proportions of caustic soda are required according to theory, whereas in practice not less than 7, and usually about 14, molecular proportions are used.

If it is attempted to carry out the fusion process by adding the alkali sulphonate to the theoretical quantity of fused caustic alkali the reaction mixture assumes an undesirable thick semi-fused condition. If, again, the theoretical quantities of alkali sulphonate, and caustic alkali are mixed together beforehand and subsequently heated to bring about the reaction, the mixture tends to froth and swell up on reaching the reaction temperature.

I have now found that it is possible to produce phenols or salts thereof from the corresponding alkali metal sulphonates by reaction with substantially the theoretical quantity of caustic alkali without the above-mentioned disadvantages, if an intimate solid mixture of the-reactants is prepared containing an additional solid particulate substance selected from the group consisting of the normal alkali metal salts of sulphurous acid and of sulphuric acid (such salts being hereinafter referred to as sulphites and sulphates, and all those salts being insoluble in fused caustic alkali) in such proportion, comprising at least 2 per cent. to about 30 per cent. of the weight of the sulphonic acid salt, that during the subsequent heating operation the reaction mixture does not froth or swell and remains in a substantially solid condition, and if the said solid mixture is heated at a temperature ranging from 350-400" C. to cause the sulphonic acid and caustic alkali to undergo reaction.

6 Claims. (Cl. 260-628) Application April 25, 1946, Serial In Great Britain September 4,

The term phenols is used herein in describing the invention to include naphthalenes and other hydroxyl-substituted aromatic or heterocyclic compounds which themselves and in the form of their corresponding sulphonates used as starting materials do not readily decompose or lead to side reaction at the reaction temperature required for the present process. Among the more especially suitable phenols there may be mentioned the hydroxy-benzenes, cresols, hydroxy-naphthalenes and hydroxy-pyridines.

The term caustic alkali as used herein and in the appended claims denotes only sodium hydro'xide or potassium hydroxide.

For convenience the added solid substances defined above will be referred to hereinafter as "anti-frothing agents. As such an anti-frothing agent I have found sodium sulphite or sodium sulphate to be especially suitable. Sodium sulphite is of special interest since it is a product of the reaction, and is therefore not foreign to the reaction.

I have also found that the reaction may be conducted with the introduction of steam, and that then, in the case of a large number of phenols, the phenol, instead of remaining in the reaction residue as a phenolate, is removed from the reaction mixture by the steam in the form of the free phenol, and can berecovered from the aqueous condensate produced by condensing the issuing vapours. By using this method of opera tion, in the case of phenols capable of being removed from the reaction mixture by the steam, only half the quantity of caustic alkali is required for the reaction, that is to say only one molecular proportion of caustic alkali for each sulphonate radical in the sulphonic acid salt. In the case of sodium benzene sulphonate and caustic soda the reaction may then be represented as follows:

However also in this case, an addition of the kind described above is necessary, for if it is attempted to conduct the reaction with the theoretical pro portion of caustic soda without such an addition, the mixture on reaching the reaction temperature suddenly swells up to form a frothy mass of great volume.

In the case of a phenol which cannot be removed by steam it remains in the reaction residue in the form of phenolate, whether steam is intro duced or not. When the reaction is conducted without steam, in the case of phenols capable of being removed by steam, the bulk of the phenol remains in the reaction residue as phenolate but a small amount is expelled as the free phenol with the water vapour produced during the reaction and may be recovered by condensing the issuing vapours. By conducting the reaction in a closed vessel so that the Water vapour cannot escape the whole of the phenol can be retained as phenolate in the reaction residue, When the reaction isconducted so as to produce a. phenolate, the latter may serve as a starting material for making other products so that it is not always necessary to convert, it into the free phenol.

revent oxidation of the reactants or of the products formed. The introduction of [steam serves as a convenient means of securing this end. Alternatively, the reaction may be conducted in an atmosphere of hydrogen or other inert gas.

When the process is applied with the introduction of steam to the manufacture of phenols, such as phenol itself, which are capable of being removed from the reaction mixture by steam, the removal of the product from the reaction vessel as it is formed with the steam constitutes a further advantage. In the case of phenols, such as resorcinol, which cannot be removed by steam, the normal theoretical quantity of caustic alkali, that is to say two molecular proportions per sulphonate radical, is required whether steam is introduced or not. The introduction of steam then serves as a convenient means for excluding air'irom the reaction vessel and also serves to remove any impurities of other phenols capable ofremoval by steam. I

In the case of phenols, such as B-hydroxypyridine, which can be removed by steam, but with greater difficulty than, say, phenol itself, a higher rate of introduction of steam is required to remove them but even then the removal is slower than in the case of phenol itself. With such phenols a better expedient is to remove a, part ofthe product with steam and recoverthe remainder from the reaction mixture. For this purpose the proportion of caustic alkali is reducedbelow the theoretical two molecular proportions per sulphonate radical to an extent appropriate to whatever proportion of theprodnot it is desired to remove by steam. For example, 1.5 mole of caustic alkali will enable 50 per cent of the p-hydroxypyridine produced to be removed by steam.

From the foregoing description it will be understood that the expression theoretical quantity of caustic alkali is used herein and in the appended claims to denote the quantity which is theoretically required under the conditions used, namely according to whether steam is introduced or not, and, inthe former case, according to the amount of the phenol removed by the steam.

The rate at which the steam is introduced will depend on the nature of the phenol and the reactivity of the mixture. In general the rate of introduction should not exceed that required to obtain a satisfactory rate of removal of the phenol so that the latter is obtained in association with as little water as possible. In general a suitable rate for the introduction of steam per hour is 3-4 times the weight of the 'sulphonate undergoing reaction, but in the case of phenols which are not very readily removed, such as fi-hydroxypyridine, a somewhat higher rate is of advantage. I

Although the use of steam is not essential in the process of the invention, its use offers the following advantages: In the case of phenols capable of being removed by steam, the theoretical quantity of caustic alkali becomes one half of that required in the absence of steam. The product is obtained in association with water only. Side reactions arereduced or avoided by the rapid removal of the phenol from the reaction mixture. A part or the whole of the heat required for the reaction may be supplied by preheating the steam. It is also found that the v v use of steamleads to a speedier reaction.

It will be understood that the reaction should be conducted in the absence of air in order to.

Operating without the introduction or" steam enables the phenolates, instead of the free ph enols, to be produced, and enables a somewhat lower reaction temperature, for example 350 C. instead 015380" C. to be used.

The particular proportion, within the afore- I said range, of the anti-frothing agent used in any particular case depends largely on the nature of theagent used. When steam is introduced 30 per cent. of sodium sulphite calculated on the weight of the sulphonate has been found adequate, and even smaller proportions may be used without seriously affecting the result.

The minimum proportions reduired to prevent frothing and maintain the reaction mixture in a substantially solid condition may be considerably below the above-mentioned percentage. Thus, in the reaction between sodium benzene sulphonate and caustic soda with the introduction of steam there may be used 15 per cent. of sodium sulphite or .15-16 per cent. of sodium sulphate. In general it is advisable, however, to. use considerably more than the minimum addition, for, while the latter prevents frothing and substantial fusion incipient fusion or sintering may occur which would hinder the removal of-thephenol when steam is used, a larger addition improves the porosity of the reaction mixture. A larger addition also facilitates the drying of the mass when the reaction mixture is worked up into the form of a granular mass as described below. Generally speaking about 2030 per cent. of the anti-irothing agent or of a mixture of two or more such agents is satisfactory, whether or not steam is used.

When an alkali sulphite is used as an antiirothing agent it may be of advantage to add also a small proportion of calcium hydroxide, since the latter gives rise to firmer granules in the case of granulation, and it serves for the subsequent causticisation of the alkali sulphite as explained hereinafter.

The reaction is considerably assisted by ensuring'that the reactants are in a state of intimate contact during the reaction. This intimate contact can be obtained very efiectively by mixing together the ingredients of the reaction mixture in the presence of water, and, while stirring the rriixture,'evaporating the water completely or sufficiently to produce a solid granular mass which will not soften or cake on heating due to the presenceof residual water. The soluble ingredients may be dissolved wholly or partially in the water before evaporating to dryness. A convenient method of mixing the ingredients in the presence of water is to mix all the ingredients, except the caustic alkali together in dry powdered form, and then mix them with a strong aqueous solution of the caustic alkali, the mixture then being evaporated to form a solid granular mass as described above. The evaporation of the water may, if desired, be carried out wholly or in its final stages in the reaction vesselbefore starting the desired intimate contact is to briquette a mix ture ofthe ingredients while in a moist condition. In each of the foregoing methods of mixing it is important to prevent the mixture from absorbing an appreciable amount of carbon dioxide from the atmosphere.

The alkali metal salt of the sulphonic acid may be the sodium or potassium salt, and a mixture of both'salts may be used. Either sodium hydroxide or potassium hydroxide may be used as the caustic alkali. The speed of the reaction is especially high in the case of potassium sulphonates, and can be increased in the case of any alkali sulphonate by the addition of a potassium salt, more especially potassium chloride. There may also be mentioned potassium sulphite or potassium sulphate, each of which also acts as an antifrothing agent. The use of a potassium salt as reaction accelerator is especially advantageous with sodium sulphonates as they do not react so rapidly as the potassium sulphonates. A very rapid reaction is obtained by reacting a potassium sulphonate with potassium hydroxide with the addition of a potassium salt which may serve both as a reaction accelerator and an anti-frothing agent. Accordingly,- an acceleration of the reaction can be secured by ensuring that the reaction mixture has a content of alkali metal radical consisting at least in part of potassium.

With regard to the reaction temperature, it has been found that when a mixture of 1 mol of sodium benzene sulphonate, 1 mol of caustic soda and 0.4 mol of sodium sulphite or sodium sulphate is heated in a current of steam phenol begins to form slowly at about 350 C. The reaction becomes rapid at about 380 C. If 0.75 mol of potassium chloride is added to the above mixture the speed of the reaction at 350 C. is about 15 times faster than it is without the potassium chloride. In general a temperature of about 380 C. gives a suitably rapid reaction. Although the most suitable reaction temperature depends to some extent on the particular sulphonate used, it will lie within the range of 350-400 C. It is of advantage to introduce the steam in preheated condition. By preheating the steam to a temperature above the reaction temperature the whole or a part of the heat required may be supplied.

Owing to the diminution in the rate at which thephenol is produced as the reactants are consumed, it is generally not of advantage to continue the reaction after about 90-95 per cent. of the sulphonate has been converted. The unchanged sulphonate can be used in a fresh treatment. If the reaction is conducted as a continuous process by charging fresh reactants into the reaction vessel to replace the materials conmined, the initial high rate of phenol production can then be substantially maintained throughout theprocess. When the process is conducted as a batch treatment with steam it is advisable to reduce the rate'of introduction of the steamto correspond with the diminution in the rate of phenol production. 'Iheinvention also includes the treatment of the reaction residue to convert alkali sulphite formed during the reaction into alkali sulphonate or caustic alkali-or both for a fresh reaction, and to recover unchanged sulphonate and any added substances.

In order to convert alkali sulphite into alkali sulphonate a solution of the iormerm ay be treated with the free sulphonic acid and the sulphur 6. dioxide formed expelled by boiling. If the sulphonic acid contains sulphuric acid thesulphate formed therefrom may be removed at a later stage. Preferably, however, the sulphuric acid removed by adding calcium hydroxide'or recovered calcium sulphite, removing the precipitated calcium sulphate by filtration, and adding alkali sulphite or alkali carbonate to the filtrate to precipitate the residual calcium sulphate. Instead of the free sulphonic acid its calcium or barium salt may be used, and the precipitated calcium or barium sulphite is then removed from the alkali sulphonate solution.

In order to convert alkali sulphite into caustic alkali a solution of the former may be boiled with calcium hydroxide or barium hydroxide. with cal cium hydroxide the conversion is only partial, but it is advantageous owing to its low cost. As is Well known the degree of causticisationdepends on the concentration of the alkali sulphite, so that by suitably adjusting the concentration the desired degree of conversion can be obtained. The unchanged alkali sulphite can be readily deposited by concentrating the solution and then removed. The unchanged sulphite so recovered may be similarly treated to convert it into caustic alkali, or re-used in the process as the antifrothlng agent. lh-e partial causticisation pr duced by calcium hydroxide may be supplemented as desired by using bariiu'n' hydroxide in addition. Other methods of conversion may be used, for example, sodium sulphite may be converted into caustic soda by electrolysis in know manner.

When the reaction is conducted in steam with complete rem-oval of the phenol formed, the reaction residue contains as soluble constituents, alkali sulphite, small quantities of'caustic alkali and unchanged alkali sulphonate together with any potassium salt which may have been added to accelerate the reaction. The reaction residue is taken up in water. In order to prepare a fresh batch of reaction mixture the resulting solution may be concentrated to cause the deposition of a quantity of the alkali sulphite such that sufficient alkali sulphite and caustic alkali remains in solution to produce the desired quantity of sulphonate by reaction With sulphonic acid oralkaline earth sulphonate as described above. To the solution obtained after removing the deposited alkali sulphite and regenerating the desired quantity of sulphonate there is added the necessary quantity of caustic alkali. The caustic alkali so added may, if desired, be made by causticisingas described above the alkali sulphite removed.

An alternative procedure is to add the required caustic alkali to the solution of the reaction residue, and then deposit by concentration and remove a quantity of alkali sulphite equal to that which has been formed during the reaction. A part of the latter is used to make the required sulphonate, and, if desired, the remainder may be used to make caustic alkali.

Another alternative is to treat the reaction residue with sufficient sulphonic acid to produce the alkali sulphonate required, and then to con- 'centrate the solution in order to'deposit the alkali sulphite, The concentrating operation may be performed before or after adding the necessary quantity of caustic alkali, but if it is performed after such addition the deposition of the alkali sulphite is facilitated since the latter is less soluble in caustic alkali solution. The alkali sulphite so removed may .be used 'for making a caustic alkali.

aisae 7- A still further alternative is to divide the reaction residue into two portions, and use one portion for making the alkali sulphonate and the other being either treated for the preparation of caustic alkali ordiscarded and replaced by fresh caustic alkali. 1

:A further and preferred method, however, is to mix the reaction residue with water, and to boil the aqueous liquor at such a concentration and with such an addition of calcium hydroxide as are necessaryto cause the formation of substantially the whole of the caustic alkali required. After filtering the liquor, the excess alkali sulphite is deposited by concentrating the filtrate and is. removed. The alkali sulphite so removed is used for preparing the necessary alkali sulphonate. The alkali sulphonate solution so obtained is then mixed with the alkaline mother liquor. After suitably concentrating the mixed solutions, the whole is evaporated to produce a fresh reaction mixture of the original composition.

'In the above methods any loss of alkali may be made good by the additionof fresh caustic alkali or alkali sulphite at a suitable stage in the procedure.

It will be understood that, when removing the excess of alkali sulphite in the above methods, sufficient sulphite should be left in the solution to serve as the anti-frothing agent in the fresh batch. If the residue contains little unchanged sulphonate and no potassium salt as reaction accelerator the excess of alkali sulphite may be removed directly in the form of solid residue.

' The aforesaid preferred method, in which the reaction residue, is causticised to produce the whole of the required caustic alkali, may be illustrated as applied to a reaction residue consisting, for example, of 18 parts of unchanged sodium benzene sulphonate, 163.5 parts of sodium sulphite and 4 parts of unused caustic alkali (the parts being by weight). The residue is dissolved inwater and the solution is adjusted to a concntration of 180 grams per litre. The solution is boiled with aboutparts of calcium hydroxide. 35 per cent. of the sulphite is causticised giving a solution containing parts of caustic soda and 107 parts of sodium sulphite. After filtration, the solution is concentrated until57 parts of sodium sulphite have been deposited, which quantity is sufficient to prepa1'e162 parts of sodium benzene sulphonate. The latter are added to the concentrate so as to produce a solution containing 180 parts of the sulphonate, 40 parts of caustic soda and parts'of sodium sulphite, which are the proportions of the constituents present in the original reaction mixture. It will be seen that only a very moderate proportion of the sodium sulphite has to be causticised to produce the whole of the caustic soda required. I

.When alkali sulphate is used as the anti-frothine agent, the above described methods of work ing up the reaction residue are also applicable with minor modifications. For example, the sulphite'will alwaysbe accompanied by sulphate, and thelatter must be retained in the system to serve as anti-frothing agent in a fresh batch of reaction mixture.

The sulphur dioxide which is liberated when alkali sulphite is treatedwith the free sulphonic acid to produce alkali sulphonate as described above may be used for making sulphuric acid for the production of sulphonic acid. When the reaction has been conducted with the introduction of steam, the quantity of sulphur dioxide so liberated is theoretically suflicient to furnish 50 per cent. of the sulphuric acid required. However, when the reaction is conducted without steam, the sulphur dioxide so liberated is preferably used for converting phenolate into free phenol as described below, and could only be used for making sulphuric acid if some other acid, for example carbonic acid, were used for the latter conversion.

I When the process is conducted without introducing steam, or when the phenol formed is not removed by the steam introduced, the phenol remains in the reaction residue in the form of the phenolate. Before working up the residue by one of the methods above described, it is desirable, to recover the phenol therefrom. For this purpose the residue may be taken up with water, and treated with an acid to decompose the phenolate. The liberated phenol may be removed in any suitable manner, for example, by simple physical separation, by distillation or by extraction with a suitable solvent. In the case of resorcinol it is advantageously extracted with ether, the ether removed from the extract solution by distillation, and the crude product purified by vacuum distillation.

Any suitable acid may be used for decomposing the phenolate, but it is preferable to use the sulphonic acid appropriate for the reaction or sulphurous acid as they are not foreign to the process. When other acids are used it is desirable, with a View to utilising the alkali salt formed to regenerate caustic alkali or sulphonate, to select an acid whose alkali salt can be causticised by calcium hydroxide or decomposed by the ap-,

.= propriatesulphonic acid. Such an acid is carbonic acid.

Prior to the treatment with acid it may be desirable to remove the bulk of the alkali sulphite, as advantage can then be taken of its low solubility in the alkaline solution.

For working up the residue after the removal of the phenol the above described methods are applicable, but there are now an'additional one equivalent of alkali salt to be dealt with and an additional one equivalent of caustic alkali to be restored.

The preferred method is to liberate the phenol by means of sulphur dioxide, and, after removing the phenol, to oausticise sufficient of the alkali sulphite with calcium hydroxide to yield the greater part or the whole of the caustic soda required. After filtration, the solution is concentrated until sufficient alkali sulphite is deposited for preparing the required amount of sulphonate.

' When the free sulphonic acid is used for preparing the sulphonate the sulphur dioxide liberated is used for decomposing the phenolate, if necessary, together with additional sulphur dioxide. The sulphonate solution and the causticised solution are combined and worked-up into a fresh reaction mixture. If an alkali sulphite is the anti-frothing agent sufficient for this purpose is left in the causticised solution. Any deficiency of caustic alkali is made up by a fresh addition thereof. This method lsmor especially suitable when alkali sulphite constitutes the whole or the greater part of the anti-frothing agent, a then the proportion of the sulphite which has to be causticised is low.

When the phenol produced is removed with steam, the mixture of the phenol and steam issuing from the reaction vessel is condensed and the condensate may be worked up by known methods for recovering and purifying the phenol. .When the phenol is insoluble or only slightly solin the process.

other phenols extraction with'benzene or a similar solvent is satisfactory, since the phenol is sub-' stantially wholly extracted thereby in a relatively dry state, and simple distillation suffices to separate and recover the solventu The residual liquor remaining after the extraction, which may contain small quantities of the and any of .the solvent which may bepresent may -either be returned to the reaction vessel with the steam or concentrated-as a residue in .the

still. In the latter case causticalkali may-be added to ensure the retention of the phenol in the still liquor. The concentrated-liquor: from the still may then be worked up by known methods for recovering the dissolved phenol.

Another method of dealin with, the residual liquor remaining after extraction is to use 'it for dissolving the reaction residue when the latter is being worked up. Any residual phenol will then be returned to the process with the reconstituted reaction mixture. During the reactionin the presence of steam the phenolate is decomposed into the free phenol and caustic alkali. i v

In some cases, for example, whenfishydroxypyridine is being made, the whole of the condensate containing the phenol=may betransierred to the still for generating steam .and at the-same timeobtaining a phenolic concentrate. Alternatively the condensate may be separately concentrated by distillingth'e water. I J

As stated above, it is desirable that the rate at which the steam is passed through the reaction vessel should be kept low so asto obtain-a condensate as rich-as possible in the phenol. In the case of some phenols a further enrichment canbe obtained by only. partially condensing theyapours from the reaction vessel so as to produce a condensate having a higher concentration of the phenol. The uncondensed steam may be re-. turned to the reaction vesselfor re-use. I I The crude phenol obtained by the foregoing methods of recovery may be purified in any suitable manner, for example, by distillation or by crystallisation from a suitable solvent.

Owing to the repeated working up'of the. reaction residue to form fresh reaction mixture-{the latter will become progressively contaminated with impurities present in the materials or'formed For example, the oxidatiojnlof. sulphite to sulphate will tend to cause the'accumulation of alkali sulphate in the mixture. The residue may therefore occasionally be treated wholly or in part by known methods to remove such impurities, or the accumulation of impuri- Example 1 100 parts of sodium benzene sulphonate. 30 parts of potassium chloride, and ,22.2; pa rts of caustic soda are mixed in aqueous solutionwith 30 parts of sodium sulphite. The mixture is evaporated'while stirring to produce a granular solid mass which does not soften on heating. The granular mass is, heated in a reaction vessel at i 380 c. in a slow current o preheated steam. [,The

;;issuingvapours are condensed to a mixture. of phenol and water. After about one'hour the production of phenol isjvery slow and about. 90i'per cent. .of the sulphonate has undergone reaction.

The-aqueous condensate is extracted with benzene, the benzene is removed from theextract solution bydistillattion, and the phenol'is recti- --fied by distillation. Approximately 45 parts of phenolare obtained, which represents ayield of 96 percentlcalculated on the sulphonate-which reacts. By-recovering the small quantity of phephenol, may be used for the'generation of st am required for the process. The residual phenol nol which remains in the aqueous liquorafter the extraction the yield is brought up to 97 percent. The residue remaining in the reaction vessel may be worked up as follows:v The residue is'dissolved in water, and the solution of mixed salts so obtained is causticised by boiling it with calcium hydroxide. The dilution of the said solutionand the quantity of calcium hydroxide added are so adjusted as to regenerate the original quantity of 22.2partsof caustic soda. After removingthe'insoluble calcium compounds byfiltration, the filtratfe is concentrated to the extent requircd'to deposit from the mother liquor the quantity of sodium sulphite needed for reaction]with.. lbenzene sulphonic acid, as described below'yfto preduce 10f) parts of sodium benzene sulphonate less such quantity of unchanged sulphonate asfmay be presentin the mother liquor. The sodium sulphite is separated from the mother liquor, dissolved in water, and treated withbenzen'e sulphonic acid to produce the requisite quantity of sodium benzene sulphonate. The solution is boiled to expel thesulphur' dioxide formed. The solution .so obtained is then mixed. with the mother liquorw'containing caustic soda; and the combined'solutions are evaporated as described above'to provide a fresh batch of granular reaction mixture. "Should the benzenesulphonic acid contain sulphuric acid additional sodium sulphite "will'be required to neutralise the latter acid, and I "this additional sulphite must be replaced by acidung fresh sulphite; the accumulationv of sodium I sulphate in the system'in this manner canwbe avoided by'discarding a portion of the separated salts. p I

I Ertample 2 H I v 100 parts of sodium benzene sulphonate;fl[30 parts of potassium. chloride and 22,2 'partsf'of causticsoda are mixed in aqueous solution with Bilparts .ofrsodium sulphate. The mixtureis evaporated while stirring to produce a granular solid mass which does not soften on heatingQ The granular mass is heated in a reaction vessel at 3801C. in a slow current of preheated steam.

' The issuing vapours are condensed to a mixture of phenol and water. After about onehou'rgthe ',production of phenol is very slow and about 90 ties may be prevented by occasionally d1scard1ng per cent. of the sulphonate has undergone reaction.

.The aqueous condensateis extracted with benzene, the benzene is removed from the extract I solution by distillation, and the phenol isrectified [by distillation, Approximately 4.5 parts of p henol are obtained, which represents a .yield of 96 per Qcenti calculated on the sulphonate whiclireacts.

' Byrecovering the small quantity of phenol which remains in the aqueous liquor after the'extraction the yield is brought up to 97 per cent.

. The residue remaining in the reaction .vessel maybe worked up as follows: The residue is, diss wed inwater, and the solution of mixedsal'ts'jso 1 .obtainedis causticised by boiling it with calcium fhydroxide. Thedilution of the said solution and K thegquan'tity Of.-.calcium hydroxide added are so sodium sulphate. The latter mixture of deposited salts is separated from the mother liquor containing caustic soda, and is then treated with a suificient quantity ,of benzene sulphonic acid to yield 100 parts of sodium benzene sulphonate less such quantity of unchanged sulphonate as may be present in the mother liquor. All the sulphur dioxide formed is expelled by boiling the solution.

The solution so obtained is then mixed with the mother liquor containing caustic soda, and the combined solutions are evaporated as described above to provide a fresh batch of granular reaction mixture.

It will be understood that the mixture of sodium sulphite and sodium sulphate must be separated from the mother liquor of caustic soda in sufficient amount to provide the quantity of sulphite required to produce 100 parts of the sulphonate upon reaction with the sulphonic acid added. Any small deficiency of sulphite can be made good by a fresh addition of sodium sulphite or the equivalent quantity of sodium carbonate. Any tendency for sodium sulphate to accumulate in the system due, for example, to sulphuric acid contained in the added sulphonic acid, may be avoided by discarding a portion of the separated salts.

Example 3 100 parts of sodium toluene sulphonate, consisting mainly of the ortho-compound, are mixed in aqueous solution with 29 parts of potassium chloride, 20.6 parts of caustic soda and 30 parts of sodium sulphite. 'The mixture is evaporated to dryness to produce a granular mass. The latter is heated in a slow current of steam at 380-390" C. After about 2 /2 hours the production of oresols becomes very slow and 90 per cent, of the sulphonate has reacted. The product which is condensed together with the steam is completely soluble in caustic soda solution.

The condensate is extracted with benzene, and the extract solution is distilled. After the distillation of the benzene, 47.5 parts of cresol are obtained by distillation for the most part at the boiling point of ortho-cresol. Only a trace of material boiling above the boiling point of paracresol is obtained. The yield of cresol exceeds 90 per cent. of the converted sulphonate.

I The solid reaction mixture is dissolved in water, and a part of the sodium sulphite is removed by crystallisation. The mother liquor is then boiled with sufficient toluene sulphonic acid to produce a total of 100 parts of the sodium salt and the necessary quantity of ,caustic soda for a further reaction is added. The solution is then evaporated to provide a fresh batch of granular reaction mixture.

. Alternatively, the reaction mixture may be worked up to regenerate the caustic alkali in the manner hereinbefore described, the calcium hydroxide required for causticisation being added for this purpose,

Example 4 [2 at a temperature of 380 C. for 5-6 hours in a slow current of steam. The condensate collected during this period contains about 3.7 parts of phenol. The reaction residue is cooled out of contact with the air, taken up with hot water, and

the aqueous mixture is filtered to remove any insoluble organic matter. The filtrate is concentrated to a small volume to facilitate the subsequent extraction, and is then neutralised by introducing sulphur dioxide gas. The mixture is again filtered to remove a little carbonaceous matter which separates, and the clear solution is exhaustively extracted with ether. After removing the ether and a little waterby distilling the ethereal solution 28 parts of a crude product are obtained which, on fractional distillation, yieldsapproximately 23.5 parts of substantially pure resorcinol leaving 4.5 parts of a by-product of high boiling point.

The aqueous mother liquor containing mainly potassium sulphite may be worked up as described in the preceding examples to prepare a fresh batch of reaction mixture.

Example 5 100 parts of sodium naphthalene a-sulphonate are mixed in aqueous solution with 24 parts of potassium chloride and 17.5 parts of caustic soda. 20 parts of sodium sulphite are added, and the whole is evaporated to produce a solid granular mass, care being taken to avoid the absorption of carbon dioxide from the atmosphere. The granular mass is then heated at 370 C. in a slow current of superheated steam, and the issuing vapours are condensed to form a mixture of anaphthol and Water. After heating for about one hour the reaction practically ceases and about per cent, of the sulphonate is converted.

The aqueous condensate is extracted with benzene, and the extract solution is distilled to remove the benzene. V The residue consists of 52 parts of a-naphthol, which represents a yield of 92 per cent. on the converted sulphonate. The product may be further purified by distillation under reduced pressure.

The reaction residue is extracted with water, and the solution is concentrated sufiiciently to remove by crystallisation a part of the sodium sulphite present. A solution of calcium naphthalene s-sulphonate is added to the mother liqnor in a quantity sufiicient to produce a total of '100 parts of the sodium sulphonate. The precipitated calcium sulphite is removed by filtration, the necessary quantity of caustic soda for a further reaction is added to the filtrate, and the latter is worked up into a granular mass as described above to provide a fresh batch of reaction mixture.

I claim:

l. A processior themanufacture of phenols or salts thereof which comprises, preparing an intimate solid mixture of an alkali metal salt of the sulphonic acid corresponding to the phenol desired, a caustic alkali in substantially the theoretical quantity and an additional particulate solid substance selected from the group consisting of the normal alkali metal salts of sulphurous acid and of sulphuric acid in such proportion, comprising at least 2 per cent. to about 30 p cent. of the weight of the sulphonic acid salt, that during the subsequent heating operation the reaction mixture does not froth or swell and remains in a substantially solid condition, and then heating the said solid mixture at a temperature 7 ranging from 350 to 400 C. to cause the sulphonic acid salt and caustic alkali to undergo reaction.

2. A process for the manufacture of phenols or salts thereof which comprises, preparing an intimate solid mixture of an alkali metal salt of the sulphonic acid corresponding to the phenol desired, a caustic alkali in substantially the theoretical quantity and an additional particulate solid substance selected from the group consisting of the normal alkali metal salts of sulphurous acid and of sulphuric acid in such proportion, comprising at least 2 per cent. to about 30 per cent. of the Weight of the sulphonic acid salt, that during the subsequent heating operation the reaction mixture does not froth or swell and remains in a substantially solid condition, and then heating the said solid mixture in a current of steam at a temperature ranging from 350 to 400 C. to cause the sulphonic acid salt and caustic alkali to undergo reaction.

3. A process for the manufacture of phenols or salts thereof which comprises, mixing together in the presence of water an alkali metal salt of the sulphonic acid corresponding to the phenol desired, a caustic alkali in substantially the theoretical quantity and an additional particulate solid substance selected from the group consisting of the normal alkali metal salts of sulphurous acid and of sulphuric acid in such proportion, comprising at least 2 per cent. to about 30 per cent. of the weight of the sulphonic acid salt, that during the subsequent heating operation the reaction mixture does not froth or swell and remains in a substantially solid condition, stirring the mixture and simultaneously evaporating sufficient water therefrom to produce a solid granular mass which is incapable both of softening and caking on heating due to the presence of water, and then heating the said granular mass in a current of steam at a temperature ranging from 350 to 400 C. to cause the sulphonic acid salt and caustic alkali to undergo reaction.

4. A process for the manufacture of phenols or salts thereof which comprises, preparing a moist mixture of an alkali metal salt of the sulphonic acid corresponding to the phenol desired, a, caustic alkali in substantially the theoretical quantity and an additional particulate solid substance selected from the group consisting of the normal alkali metal salts of sulphurous acid and of sulphuric acid in such proportion, comprising at least 2 per cent. to about 30 per cent. of the weight of the sulphonic acid salt, that during the subsequent heating operation the reaction mixture does not froth or swell and remains in a substantially solid condition, forming the moist mixture into briquettes, and then heating the said briquettes in a current of steam at a temperature ranging from 350 to 400 C. to cause the sulphonic acid salt and caustic alkali to undergo reaction.

5. A process for the manufacture of phenols or salts thereof which comprises, preparing an intimate solid mixture of an alkali metal salt of the sulphonic acid corresponding to the phenol desired, a caustic alkali in substantially the theoretical quantity and an additional particulate solid substance selected from the group consisting of the normal alkali metal salts of sulphurous acid and of sulphuric acid in such proportion, comprising at least 2 per cent. to about 30 per cent. of the weight of the sulphonic acid salt, that during the subsequent heating operation the reaction mixture does not froth or swell and remains in a substantially solid condition, preparing the said solid mixture so that it includes a content of alkali metal radical consisting at least in part of potassium, and then heating the said solid mixture at a temperature ranging from 350 to 400 C. to cause the sulphonic acid salt. and caustic alkali to undergo reaction.

6. A process for the manufacture of phenols or salts thereof which comprises, preparing-an intimate solid mixture of an alkali metal salt of the sulphonic acid corresponding to the phenol desired, a caustic alkali in substantially the theo-- retical quantity and an additional particulate solid substance selected from the group consisting of the normal alkali metal salts of sulphurous acid and of sulphuric acid in such proportion, comprising at least 2 per cent. to about 30 per cent. of the weight of the sulphonic acid salt, that during the subsequent heating operation the reaction mixtur does not froth or swell and remains in a substantially solid condition, preparing the same solid mixture so that it includes a content of alkali metal radical consisting at least in part of potassium, and then heating the said solid mixture in a current of steam at a temperature ranging from 350 to 400 C. to cause the sulphonic acid salt and caustic alkali to undergo reaction.

DANIEL TYRER.

REFERENCES CITED The following references are of record in the file of this patent:

UNITED STATES PATENTS Number Name Date 1,179,415 Ellis Apr. 18, 1916 1,191,880 Ellis July 18, 1916 1,210,726 Tyrer Jan. 2", 1917 1,274,961 Wallach Aug. 6, 1918 1,312,127 McKee Aug. 5, 1919 1,820,274 Hempel Aug. 25, 1931 FOREIGN PATENTS Number Country Date 141,440 Great Britain 1920 559,642 Great Britain May 15, 1944 811,240 France Apr. 9, 1937 

